1. Field of the Invention
The present invention relates to a liquid crystal display, and more particularly, to a multi-domain liquid crystal display preventing deviation of a domain boundary using a patterned spacer.
2. Discussion of the Related Art
A liquid crystal panel as a main element of a liquid crystal display includes a first substrate having color filters and a common electrode formed thereon, a second substrate having a TFT array and pixel electrodes formed thereon so as to leave an interval from the first substrate, and liquid crystals injected between the first and second substrates. In this case, alignment layers are formed between the first substrate and liquid crystals and between the second substrate and liquid crystals, respectively so as to anchor uniformly the liquid crystals adjacent to surfaces of the alignment layers thereto. When the liquid crystals adjacent to the first and second substrates are uniformly anchored in a predetermined direction, distribution of the liquid crystal molecules constitutes a structure of a liquid crystal layer having the most stable state by elasticity of the liquid crystal molecules. In other words, the structure of the liquid crystal layer depends on the alignment characteristics of the alignment layers of the first and second substrates. In this case, each alignment characteristic of the respective substrates can be expressed by an alignment direction and a pretilt angle of the corresponding alignment layer.
An alignment process method for the alignment layer formed on the substrate is mainly a rubbing method. The rubbing method applies a mechanical force to the alignment layer formed on the substrate in a predetermined direction using a cloth, thereby enabling to perform an alignment process simply and quickly.
Even though being useful for giving a single alignment direction to the alignment layer on the substrate, the rubbing method has difficulty in carrying out the alignment process on the single alignment layer on the substrate to have various alignment directions.
Each of the alignment layers on the first and second substrates is made to have one alignment direction, the first and second substrates are bonded to each other so that the alignment layers confront each other, and liquid crystals are injected between the first and second substrates. Thus, a uniform mono-domain liquid crystal panels is prepared. In this case, in accordance with the arrangement of the alignment directions of the first and second substrates, the liquid crystal layer has a twist structure or parallel configuration. Yet, the mono-domain liquid crystal panel has an asymmetrical characteristic of a viewing angle as well as an area having a bad photo characteristic. Namely, an area having gray inversion or bad contrast ratio is generated in accordance with the viewing angle.
Therefore, in order to improve the viewing angle characteristics of the liquid crystal panel, proposed are multi-domain liquid crystal panels such as TDTN (two domains TN)-LCD and the like. The multi-domain liquid crystal panel is fabricated by carrying out an alignment process thereon so as to provide at least two different alignment directions of alignment layers on two confronting substrates.
A general multi-domain liquid crystal and fabricating method thereof according to a related art are explained in detail by referring to the attached drawings as follows.
FIG. 1A illustrates a layout of a liquid crystal display according to a related art, and FIG. 1B illustrates a cross-sectional view along a cutting line I–I′ in FIG. 1A.
Referring to FIG. 1A and FIG. 1B, a general multi-domain liquid crystal display includes a plurality of gate lines 1 formed on a first substrate 9 in one direction so as to leave a predetermined interval from each other and a plurality of data lines formed in a direction vertical to the gate lines 1 respectively so as to define a plurality of pixel areas. A plurality of pixel electrodes 8 are formed on the pixel areas, respectively, and a plurality of thin film transistors (TFT) 7 are formed on intersections where the gate and data lines 1 and 3 cross with each other so as to apply data signals of the data lines 3 to the pixel electrodes 8 in accordance with scan signals of the gate lines 1, respectively. And, a first alignment layer 17a is formed on an entire surface of the first substrate including the pixel electrodes 8.
A black matrix layer 14 is formed on a second substrate 10 so as to cut off lights from a portion except the pixel areas, and R, G, and B color filter layers 15 are formed on portions corresponding to the respective pixel areas so as to realize colors. A common electrode 16 is formed on entire surfaces of the R, G, and B color filter layers 15, and a second alignment layer 17b is formed on the common electrode 16.
The above-constituted first and second substrates 9 and 10 secure a predetermined space by a ball spacer 6 so as to be bonded to each other by a sealant (not shown in the drawings).
A liquid crystal layer 18 is formed in a space between the bonded two substrates.
As mentioned in detail in the foregoing explanation, in a case of the mono-domain liquid crystal panel of which alignment states of the first and second alignment layers are uniform, there are problems such as the asymmetric viewing angle characteristic, the area having gray inversion according to the viewing angle, the reduced contrast ratio, and the like. Hence, it is necessary to fabricate a multi-domain liquid crystal panel having different alignment states in an area divided into at least two sub-areas in the same cell.
In order to fabricate the multi-domain liquid crystal panel, as shown in FIG. 1A and FIG. 1B, the pixel area on the first substrate 9 is divided into first and second alignment areas so that the first alignment layer 17a has different alignment states, and the other pixel area on the second substrate 10 is divided into third and fourth alignment areas so that the second alignment layer 17b has different alignment states. Namely, a first domain area is determined by the first alignment are of the first alignment layers 17a and the third alignment area of the second alignment layer 17b, and a second domain area is determined by the second alignment area of the first alignment layer 17a and the fourth alignment area of the second alignment layer 17b. 
An alignment method for the first to fourth alignment areas is explained by referring to the attached drawings as follows.
FIG. 2A and FIG. 2B illustrates cross-sectional views along a cutting line II–II′ in FIG. 1A for explaining an alignment method of a general multi-domain liquid crystal display, and FIG. 3 illustrates a schematic cross-sectional view along the cutting line II–II′ in FIG. 1A.
For a method of forming alignment layers, an alignment material such as polyimide is coated on the first substrate 9 having finished TFT array and pixel electrode processes and the second substrate 10 on which the common electrode is formed, thereby forming the first and second alignment layers 17a and 17b. The first and second alignment layers 17a and 17b, as shown in FIG. 2A, are then rubbed for first alignment.
Referring to FIG. 2B, a photo-mask 20 is selectively formed on portions of the first and second alignment layers 17a and 17b of the first and second substrates 9 and 10 corresponding to the second and third alignment areas in FIG. 1B. UV-rays are irradiated on the first and fourth alignment areas selectively so as to reduce pretilt angles of the first and second alignment layers 17a and 17b. 
After completion of the alignment process, a ball spacer 6 is scattered on the first or second substrate 9 or 10. A sealant (not shown in the drawing) is printed on the first or second substrate 9 or 10 so as to bon the first and second substrates to each other. Liquid crystals are then injected between the first and second substrates.
Namely, alignment areas having greater pretilt angles in domains alternate with each other, whereby directions of mean liquid crystal molecules are distributed so as to be opposite to each other. When an electric field is applied thereto, as shown in FIG. 3, main viewing angle directions of two domains become opposite to each other so as to compensate the viewing angle thereof.
In this case, if a boundary between the areas having the alignment states different from each other is called an alignment boundary 4, the alignment directions of the mean liquid crystal molecules should be different from each other centering around the alignment boundary 4 in the above-constituted multi-domain liquid crystal display. Since the alignment directions of the mean liquid crystal molecules are different from each other centering around the alignment boundary, light leakage may be generated from a portion corresponding to the alignment boundary 4. In order to prevent the light leakage of the alignment boundary 4, the black matrix layer 14a is formed on the second substrate 10 corresponding to the alignment boundary 4.
Yet, referring to FIG. 1A and FIG. 1B, the alignment directions of the mean liquid crystal molecules fail to differ in directions from each other at the alignment boundary 4, but the first domain area crosses the alignment boundary 4 so as to expand to a portion A adjacent to the alignment boundary 4.
Therefore, a boundary from which the real alignment directions of liquid crystals becomes a real domain boundary 5 failing to coincide with the alignment boundary 4.
When the alignment boundary 4 fails to coincide with the real domain boundary 5, the black matrix layer 14a for preventing the light leakage of the alignment boundary 4 fails to prevent light leakage from the real domain boundary (disclination line) 5.
Since the light leakage from the real domain boundary 5 fails to be prevented, a contrast ratio is decreased. Moreover, an opening ratio is reduced if the black matrix layer 14a is formed wider to consider the above problem.
Thus, the major factor of generating the mismatch between the alignment boundary 4 and the real domain boundary 5 is the ball spacer 6 formed at the portion adjacent to the alignment boundary 4.
In this case, the ball spacer 6 is formed in a manner that plastic or silica balls, each having a demanded size, are scattered on a substrate. Spacer balls are dispersed in an organic solvent, and then the spacer 6 and organic solvent adhere to the surface of the substrate using an air pressure. Flon was previously used as the organic solvent, but is restricted or ceases to use for the protection of global environment. Therefore, replacement solvents and dry scattering methods are developed so as not to use the organic solvent. And, uniformity improvement of the spacer 6 in distribution density, bonding prevention, enhancement of adhesiveness between upper and lower plates as well as large-sized product and high resolution become current issues for LCD fabrication.
Besides, a panel of which pixel pitch is 20˜30 μm like a liquid crystal projector uses a black resin spacer 6 since a contrast ratio is reduced by light leakage at a portion where the spacer 6 exists.
As mentioned in the above explanation, the spacer 6 is scattered so as to maintain a uniform gap (height) between upper and lower plates of LCD according to the related art. The scattered spacer 6 fails to precisely coincide with the alignment boundary 4 in the multi-domain LCD. Therefore, the director of the liquid crystals is influenced by the spacer 6 so that the domain boundary 5 fails to coincide with the alignment boundary 4.
Namely, in case of using the first and second alignment layers 17a and 17b fabricated by the above method, the alignment boundary 4 should coincide with the domain boundary 5 at the pixel electrode. Yet, as shown in FIG. 1A and FIG. 1B, the alignment boundary 4 deviates from the domain boundary 5 so that the domain boundary 5 is formed around the spacer 6. When the general spacer 6 is scattered on the first or second substrate 9 or 10, the domain boundary 5 fails to coincide with the alignment boundary 4 as well as is formed around the spacer 6. Therefore, the contrast ratio of the pixel is reduced. This means that the domain boundary is misaligned since the randomly scattered spacer 6 has influence on the alignment boundary 4. In order to overcome this misalignment of the domain boundary, required is a spacer arranged regularly as well as enabling to minimize the influence on the pixel electrode.